netdev - Re: Socket buffer sizes with autotuning

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Message-Id: <20080507.184311.196815718.davem@davemloft.net>
Date:	Wed, 07 May 2008 18:43:11 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	hkchu@...gle.com
Cc:	netdev@...r.kernel.org
Subject: Re: Socket buffer sizes with autotuning

From: "Jerry Chu" <hkchu@...gle.com>
Date: Wed, 7 May 2008 18:37:01 -0700

> Ok, will give it a try. First i'll fix your patch to
> atomic_add()/atomic_sub() by
> skb_shinfo(skb)->gso_segs rather than always 1, in order for GSO/TSO to work.

That might not work.  gso_segs can change over time as retransmit
packets get split up due to SACKs etc.  it needs to be audited,
at the very least.

> One problem came up to my mind - it seems possible for __kfree_skb() to
> access skb_shinfo(skb)->in_flight whose tp has been freed up since only the
> original skb's on TCP's rexmit list have the owner set and socket
> held. One solution
> is for TCP to zap skb_shinfo(skb)->in_flight field when it's ready to
> free up skb.
> I can hack sock_wfree() to do this, but I don't know how to do it right.

There will be references to the socket, so this should be ok.

If it isn't we can adjust the count and zap the pointer in
skb_orphan().
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